A Genetic Dissection of the Incomplete Penetrance of RPSA Variants for Isolated Congenital Asplenia

/ABSTRACT Isolated congenital asplenia (ICA) is characterized by the absence of a spleen at birth without any detectable associated developmental abnormalities (OMIM #271400). It is a life-threatening disorder, as affected patients are prone to invasive bacterial disease, especially prior to the diagnosis of ICA. We previously discovered germline heterozygous variants in the coding region and 5'UTR of RPSA (encoding ribosomal protein SA) as the first genetic etiology of ICA, and demonstrated that RPSA haploinsufficiency underlies autosomal dominant ICA. Follow-up analysis of the splenic relatives of ICA patients in our cohort revealed that some coding RPSA variants and all 5'UTR RPSA variants display incomplete penetrance for ICA. We now hypothesize that sufficiently high levels of wild-type (WT) RPSA expression may compensate for deleterious RPSA variants, and that variation in WT RPSA expression between individuals underlies the observed incomplete penetrance. Furthermore, we hypothesize that variants in the 5'UTR of RPSA impair, but do not ablate, the translation of RPSA mRNA, thereby lowering the threshold of WT RPSA expression required to compensate and explaining why the observed 5'UTR variants all lead to ICA with incomplete penetrance. To test our hypothesis, we will first assess the impact of the 5'UTR variants on RPSA translation using ribosome-profiling, polysome analyses, and mRNA secondary structure probing and mutagenesis experiments. We will then search for sequence variation between the splenic and asplenic members of our cohort at genetic positions that modulate the expression of WT RPSA. Finally, we will develop assays to precisely quantify the allele specific expression of RPSA mRNA and then compare WT RPSA mRNA expression between splenic and asplenic carriers of deleterious RPSA variants. We have already sequenced the whole genome of 69 RPSA heterozygotes in our cohort. Our preliminary data are exciting, as we have delineated three haplotypes at the WT RPSA locus that seem to tightly correlate with the presence or absence of a spleen in individuals heterozygous for a variant RPSA allele. An understanding of why some RPSA genotypes lead to ICA with incomplete penetrance will prove useful in our understanding of a life-threatening immunodeficiency, and will provide a roadmap for the study of incomplete penetrance in other genetic diseases driven by haploinsufficiency. I am an MD/PhD student at the Weill Cornell/Memorial Sloan Kettering/Rockefeller Tri-Institutional Program, performing the proposed research in the laboratory of Dr. Jean-Laurent Casanova at The Rockefeller University. My long-term goal is to become a physician scientist who balances patient care with running an independent research program at an academic institution. The plan outlined in this proposal, along with the support and mentorship provided by Dr. Casanova, Dr. Boisson, my thesis research committee, and the Tri-Institutional administrative faculty will help me achieve my career goals. Project Number: 1F30HD116571-01A1 | Fiscal Year: 2025 | NIH Institute/Center: Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) | Principal Investigator: Haralambos Mourelatos | Institution: WEILL MEDICAL COLL OF CORNELL UNIV, NEW YORK, NY | Award Amount: $54,538 | Activity Code: F30 | Study Section: Special Emphasis Panel[ZRG1 F08-L (20)] View on NIH RePORTER: https://reporter.nih.gov/project-details/1F30HD11657101A1